1. Field of the Invention
The invention relates generally to the field of electrical communications and specifically to traffic and vehicle communications. A traffic signal control system employs a controller and a plurality of remote control units, each having the capability of altering the normal sequence of traffic signal lights at an intersection. Each controller has the capability of acting as primary or secondary controller and can assume control from the primary controller when serving as the back-up unit.
2. Description of the Prior Art
Control of traffic signal lights has been undertaken by a variety of means extending from mechanical timers to computers. The fundamental goal of traffic light control is to accurately route cross-traffic through an intersection, and with increasing sophistication of control systems, it is the further goal to optimize traffic flow along an entire length of roadway. Also, an ideal traffic control system is able to accomodate special traffic conditions such as the passage of an emergency vehicle by anticipating the path of the vehicle and providing a clear right-of-way through all intersections. Although many systems have been proposed to meet these goals, few have found success. The primary causes for failure are that some systems are overly complicated for existing technology and therefore are unreliable or overly expensive, or others are too simple and may be tampered with by unauthorized persons for their own benefit.
The prior art includes U.S. Pat. No. 3,828,307 to Hungerford, relating to a central computer controlled system wherein the computer is linked by a telephone line to several remote terminals, each of which controls a traffic light. U.S. Pat. No. 3,881,169 to Malach discloses a traffic controller that is capable of detecting an audio signal from an emergency vehicle to alter the lights at the intersection in favor of the vehicle's right-of-way. U.S. Pat. No. 3,920,967 to Martin et al. teaches a computer controlled traffic light system wherein detectors monitor traffic flow and report to the computer so that traffic flow through a network of intersection traffic lights can be optimized. U.S. Pat. No. 4,016,532 to Rose suggests controlling the light latches associated with traffic light signals for emergency purposes by broadcasting a binary coded signal that is received and compared for a signal match, after which the light latch is operated. Finally, U.S. Pat. No. Re. 28,100 to Long and U.S. Pat. No. 3,831,039 to Henschel are relevant to a traffic light control system wherein a stroboscopic light on an emergency vehicle signals the vehicle approach to a traffic light, and various signal recognition safeguards in the light controller prevent unintended activation of the emergency control mechanism.
The above art indicates that the problems of providing right-of-way for an emergency vehicle have been dealt with through a variety of approaches; but in all cases the traffic light control system has to some extent required the emergency vehicle to make its presence known as distinguished from other vehicles. Traffic light controllers otherwise respond in a predetermined manner or within limited parameters to locally detected conditions, based on standard programming and operating sequences. The present invention seeks to expand the versatility of special purpose traffic light control by allowing remote control of traffic lights under circumstances of unusual local traffic flows.
A complex encoding method is proposed that on one hand will prevent unauthorized remote manipulation of traffic signals, while at the same time offering simplicity and low cost for establishing a new code in the event that an unauthorized use is discovered. Also, the reliability of traffic light controllers is increased through provision for redundancy of controllers.